The technical problems of video use control such as video copy inhibition and copy control are well known. These are techniques to prevent or discourage unauthorized copying of typically copyrighted movies or television programs or other video material. An example of copy inhibition is disclosed in Ryan U.S. Pat. No. 4,631,603, incorporated herein by reference in its entirety, wherein an analog video signal is modified so that a television receiver will still provide a normal color picture from the modified video signal, while a video tape recording of the modified video signal when replayed produces generally unacceptable television pictures. This “AGC” method relies on the fact that particular video cassette recorder (VCR) automatic gain control systems cannot distinguish between normal “sync” (synchronization) pulses of a conventional video signal and added “pseudo-sync” pulses. Ryan discloses adding pseudo-sync (negative going) pulses paired with positive going (“automatic gain control”) pulses in the vertical blanking intervals in order to result in unacceptable picture quality during playback of a recorded analog video signal. Another type of copy inhibition (also for analog video) is disclosed in Ryan U.S. Pat. No. 4,577,216 and Wrobleski et al. U.S. Pat. No. 6,516,132 both incorporated by reference in their entirety and disclosing what is called the “color stripe” (CS) process wherein the color burst conventionally present in the horizontal blanking interval on each line of active color video (in the analog domain) is modified in terms of its phase so that any subsequent video tape recording of the video signal shows undesirable variations in the color fidelity that appear as bands or stripes of color error.
Another type of analog video copy inhibition is in Ryan U.S. Pat. No. 4,819,098 also incorporated by reference in its entirety disclosing what is referred to here as the “back porch pulse” (“BPP”) process or modification wherein a positive going pulse is added to the video signal immediately following a trailing edge of normally occurring horizontal synchronization pulses, hence being in the horizontal sync pulse's back porch region. (In this context positive going refers to the standard video waveform where the horizontal synchronization pulses are negative going, with their back porches being in NTSC-TV at an amplitude of 0 IRE units in the active video portion of the video signal, and their lowest part extending down to an amplitude of about −30 IRE units.) The back porch pulses typically have an amplitude of about the same level as the peak white level in the active video but brief duration, e.g. 4 microseconds, to achieve the maximum anti-copy effect. In one commmercialized version of this BPP process, up to 15 such pulses are added (chiefly in the vertical blanking interval—VBI) prior to the vertical synchronization broad pulses and up to 15 such pulses are added after the vertical synchronization broad pulses, in each frame of video. (In NTSC-TV, the VBI extends from video scan line 1 to line 21 but the back porch pulses may be added also in active video in the overscan part of the picture.) The BPP process is compatible with NTSC, PAL, and SECAM television as are the AGC and CS processes.
Also well known are various copy control techniques suitable for use with either analog or digital video wherein typically a watermark or some other coded data is included in a video signal and is detected by an especially adapted video recorder. The video recorder upon detecting the watermark or coded data either permits or does not permit copying. In some cases generational (e.g., copy once only) copy control is thereby provided.
However, further copy prevention problems are presented when, for instance, analog video is subsequently recorded (stored) in digital form. This is referred to as the analog video interface. For instance, there is a problem which occurs with what are called, in the video field, personal video recorders (PVR) of the type sold by Replay TV and TiVo. These digital storage devices (which include a hard disk drive) enable digital recording of broadcast TV, cable TV or other analog video signals. The digital signal processing circuitry of these devices typically strips off any of the above described analog copy inhibition signals which are present in the blanking intervals. (Note that many digital video recorders similarly do not record the blanking intervals.) In the context of copyrighted video material such as television programs, movies, etc. the copyright owners want to control or prevent such copying (storage) using a PVR or similar type device. Note that in this context PVR devices include not only the standalone PVR devices of the type disclosed above but also, for instance, DVD recorders and personal computers which may include (or not include) a television tuner and which therefore can function the same as a PVR in recording incoming video on their hard disk drive or other type of digital storage.